An apple a day may not only keep the doctor away, it could also keep dementia at bay.

Apples and apple juice prevent some of the cell damage in the brain that may lead to Alzheimer's disease in old age, according to one study. The fruit's protective power comes from antioxidants, chemicals that are known to protect cells throughout the body, particularly the brain and the heart.

Antioxidants do their work in the body by disarming cell-damaging free radicals, reactive rogue molecules of oxygen that attack the membrane covering of all cells and the DNA that contains a cell's basic operating instructions. Free radicals are implicated in heart disease because they oxidize the "bad" cholesterol, leading to hardened arteries.

By damaging the genetic machinery of cells, free radicals also are thought to contribute to the development of cancer and a number of degenerative conditions including Parkinson's disease. Free radicals enter our bodies through pollution, fried foods and the normal metabolic processes of the body.

University of Massachusetts in Lowell scientists fed apple extracts to mice to test whether the fruit is protective against the brain damage caused by free radicals in aging mice. They compared two groups of lab animals, both fed a nutrient-deficient diet. However, one group was given apple juice concentrate in its water.

The mice that consumed the apple juice subsequently outperformed the other mice in maze tests. The apple juice group also had less oxidative brain damage than the other mice. The findings were published in the Journal of Alzheimer's Disease.

Thomas B. Shea, director of the University of Massachusetts Lowell's Center for Cellular Neurobiology and Neurodegeneration Research, said the findings are encouraging for anyone who is interested in staying mentally sharp as they grow older. The mice were given the human equivalent of two to three cups of apple juice or two to four apples per day. The researchers believe that whole fruits and vegetables may provide more antioxidant punch than purified antioxidant supplements sold as pills.

Previous studies have found apples to be high in a particular antioxidant called quercetin. It's not just a boon to the brain; studies have shown quercetin may reduce cancer risk, prevent heart attacks, stave off cataracts, prevent recurrent gout attacks and speed healing from acid reflux disease.

While apples are no silver bullet for Alzheimer's, or any other disease for that matter, the research suggests there's no downside to eating apples. Fresh whole apples are the best form of the fruit as quercetin is found primarily in apple skin. Red apples generally have more of the antioxidant than green apples.

Apples aren't your thing? Load up on cranberries, blueberries or onions. Each is also loaded with brain-protecting quercetin.